让我先说这是对
this topic的后续问题.
通过从Solaris(SmartOS)切换到用于memcached服务器的Ubuntu,“解决了”.现在我们将负载乘以约5倍,并再次遇到问题.
我们正在运行一个大约1000个请求/分钟的站点,每个请求命中Memcached大约3次读取和1次写入.因此负载大约是每秒65个请求.缓存中的总数据大约为37M,每个密钥包含非常少量的数据(JSON编码的整数数组小于1K).
我们在这些页面上设置了基准测试脚本,并将数据输入StatsD进行日志记录.问题是Memcached需要很长时间才能响应.这些似乎与流量高峰无关.
什么可能导致这些尖峰？为什么memcached会接管一秒钟回复？我们刚刚启动了第二台服务器进入池中,并没有在峰值的频率或严重程度上产生任何明显的差异.
这是服务器上getStats()的输出：
Array
(
[-----------] => Array
(
[pid] => 1364
[uptime] => 3715684
[threads] => 4
[time] => 1336596719
[pointer_size] => 64
[rusage_user_seconds] => 7924
[rusage_user_microseconds] => 170000
[rusage_system_seconds] => 187214
[rusage_system_microseconds] => 190000
[curr_items] => 12578
[total_items] => 53516300
[limit_maxbytes] => 943718400
[curr_connections] => 14
[total_connections] => 72550117
[connection_structures] => 165
[bytes] => 2616068
[cmd_get] => 450388258
[cmd_set] => 53493365
[get_hits] => 450388258
[get_misses] => 2244297
[evictions] => 0
[bytes_read] => 2138744916
[bytes_written] => 745275216
[version] => 1.4.2
)
[-----------:11211] => Array
(
[pid] => 8099
[uptime] => 4687
[threads] => 4
[time] => 1336596719
[pointer_size] => 64
[rusage_user_seconds] => 7
[rusage_user_microseconds] => 170000
[rusage_system_seconds] => 290
[rusage_system_microseconds] => 990000
[curr_items] => 2384
[total_items] => 225964
[limit_maxbytes] => 943718400
[curr_connections] => 7
[total_connections] => 588097
[connection_structures] => 91
[bytes] => 562641
[cmd_get] => 1012562
[cmd_set] => 225778
[get_hits] => 1012562
[get_misses] => 125161
[evictions] => 0
[bytes_read] => 91270698
[bytes_written] => 350071516
[version] => 1.4.2
)
)
编辑：这是设置和检索10,000个值的结果.
正常：
Stored 10000 values in 5.6118 seconds. Average: 0.0006 High: 0.1958 Low: 0.0003 Fetched 10000 values in 5.1215 seconds. Average: 0.0005 High: 0.0141 Low: 0.0003
当Spiking：
Stored 10000 values in 16.5074 seconds. Average: 0.0017 High: 0.9288 Low: 0.0003 Fetched 10000 values in 19.8771 seconds. Average: 0.0020 High: 0.9478 Low: 0.0003
网络堆栈可能存在问题.我有类似memcached的问题,原因是用尽了linux conntrack处理程序. 你能检查尖峰之前和之后的netstat -s -t输出来检查tcp错误和重新发送.您还可以尝试使用wireshark查看流量转储以获取有关该问题的更多信息.
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